In oil-based fluids, the continuous or external phase is typically diesel oil. When immiscible water is emulsified and suspended as the dispersed or internal phase, the fluid is typically referred to as an invert emulsion fluid. True oil-based invert emulsion fluids are formed by the emulsification of brine water. Excellent descriptions of oil-based invert emulsion fluids are found in the following two articles: (1) R. B. Bennet, Journal of Petroleum Technology "New Drilling Fluid Technology--Mineral Oil Mud" pp 975-981 (1984), and (2) P. A. Boyd, et al. Journal of Petroleum Technology "New Base Oil Used in Low--Toxicity Oil Muds" pp 137-142 (1985).
Oil-based invert emulsion type fluids are widely used in a diversity of well working applications. They are ideally suited to deep wells, of high temperature and pressure. They provide the highest probability of drilling holes in areas of known instability. They prevent dissolution and serious erosion when drilling water-soluble formations. And, they also exhibit superior lubricity qualities in directional and horizontal wells as compared to water-based fluids.
Despite the many advantages of oil-based invert emulsion muds, their use has been limited by environmental concerns. Prior art invert emulsion oil muds tend to be toxic to marine life due to their high concentrations of aromatics. Environmental regulations for offshore drilling fluids now require bioassays to determine whether the fluid meets established toxicity limits for discharge into the seas. The bioassay protocol concerns the toxicity of the drilling fluids to mysid shrimp, Mysidopsis bahia, which is indigenous to warm bay waters in the Gulf of Mexico. The protocol is in accordance with Federal Register, Vol. 50, No. 165, pages 34632-34636.
The advantages of using invert emulsion oil muds in difficult drilling situations, and the environmental concerns associated with their use, has led researchers to pursue the development of non-hydrocarbon oil muds. Essentially this pursuit has involved the replacement of diesel oil with more environmentally acceptable liquids. One such replacement liquid which has found commercial acceptance is mineral oil, a low polynuclear aromatic (LPNA) oil. The problem with mineral oil-based muds is that even though mineral oil is more environmentally acceptable than diesel oil, it is still an oil. The regulations governing the amount of oil allowed to be discharged into the sea along with drilled cuttings are becoming even more stringent leading researchers to pursue synthetic materials to replace the use of all petroleum based oils, including mineral oil.
Ideal oil replacement liquids should cause low or no sheen or discoloration of surface water, have low toxicity to marine and freshwater organisms, have a high flashpoint range to assure safe operation of the system, and be capable of forming a good, stable, invert emulsion drilling mud.
Suitable non-oil replacement liquids are taught in U.S. Pat. Nos. 5,057,234 and 5, 141,920 and include polypropylene glycols, polypropylene glycol ethers, and propylene oxide polymeric adducts of alcohols or mixtures of alcohols. The present invention provides additional non-oil replacement liquids for invert emulsion fluids.
The invert emulsion fluids of this invention comprise non-hydrocarbon, non-mineral oil continuous phase materials which have high flashpoints and meet the stringent EPA toxicity limits for discharge into sea water as measured by the bioassays of mysid shrimp.